This invention relates to trenchless rehabilitation of existing conduits and pipelines, and more particularly to installation of cured in place liners having an inner impermeable layer by pulling in and inflating.
It is generally well known that existing conduits and pipelines, particularly underground pipes, such as sanitary sewer pipes, storm sewer pipes, water lines and gas lines that are employed for conducting fluids frequently require repair due to fluid leakage. The leakage may be inward from the environment into the interior or conducting portion of the pipelines. Alternatively, the leakage may be outward from the conducting portion of the pipeline into the surrounding environment. In either case of infiltration or exfultration, it is desirable to avoid this type of leakage.
The leakage in the existing conduit may be due to improper installation of the original pipeline, or deterioration of the pipe itself due to normal aging, or the effects of conveying corrosive or abrasive material. Cracks at, or near pipe joints may be due to environment conditions such as earthquakes, or the movement of large vehicles on the overhead surface, or similar natural or man-made vibrations, or other such causes. Regardless of the cause, such leakages are undesirable and may result in waste of the fluid being conveyed within the pipeline, or result in damage to the surrounding environment and possible creation of dangerous public health hazards. If the leakage continues it can lead to structural failure of the existing conduit due to loss of soil and side support of the conduit.
Because of ever increasing labor and machinery costs, it is increasingly more difficult and less economical to repair underground pipes or portions that may be leaking by digging up the existing pipe and replacing the pipe with a new one. As a result, various methods have been devised for the in place repair or rehabilitation of existing pipelines. These new methods avoid the expense and hazards associated with digging up and replacing the pipe or pipe sections, as well as the significant inconvenience to the public during construction. One of the most successful pipeline repair or trenchless rehabilitation processes that is currently in wide use is called the Insituform® Process. The Insituform Process is described in detail in U.S. Pat. No. 4,009,063, U.S. Pat. No. 4,064,211 and U.S. Pat. No. 4,135,958, the contents of which are all incorporated herein by reference.
In the standard practice of the Insituform Process an elongated flexible tubular liner of a felt fabric, foam or similar resin impregnable material with an outer impermeable coating that has been impregnated with a thermosetting curable resin is installed within the existing pipeline. In the most widely practiced embodiment of that process, the liner is installed utilizing an eversion process, as described in the '211 and '958 Insituform patents. In the eversion process, radial pressure applied to the interior of an everted liner presses it against and into engagement with the inner surface of the pipeline as the liner unfolds along the length of the pipeline. The Insituform Process is also practiced by pulling a resin impregnated liner into the conduit by a rope or cable and using a separate fluid impermeable inflation bladder or tube that is everted within the liner to cause the liner to cure against the inner wall of the existing pipeline. Such resin impregnated liners are generally referred to as “cured-in-place-pipes” or “CIPP liners” and the installation is referred to a CIPP installation.
Conventional cured in place flexible tubular liners for both the eversion and pull-in-and-inflate CIPP installations have an outer smooth layer of relatively flexible, substantially impermeable polymer coating in its initial state. The outer coating allows a resin to be impregnated into the inner layer of resin impregnable material, such as felt. When everted, this impermeable layer ends up on the inside of the liner with the resin impregnated layer against the wall of the existing pipeline. As the flexible liner is installed in place within the pipeline, the pipeline is pressurized from within, preferably utilizing an eversion fluid, such as water or air to force the liner radially outwardly to engage and conform to the interior surface of the existing pipeline. Cure of the resin is initiated by introduction of hot curing fluid, such as water into the everted liner through a recirculation hose attached to the end of the everting liner. The resin impregnated into the impregnable material then cures to form a hard, tight fitting rigid pipe lining within the existing pipeline. The new liner effectively seals any cracks and repairs any pipe section or pipe joint deterioration in order to prevent further leakage either into or out of the existing pipeline. The cured resin also serves to strengthen the existing pipeline wall so as to provide added structural support for the surrounding environment.
When tubular cured in place liners are installed by the pull-in-and-inflate method, the liner is impregnated with resin in the same manner as in the eversion process and pulled into and positioned within the existing pipeline in a collapsed state. In a typical installation, a downtube, inflation pipe or conduit having an elbow at the lower end is positioned within an existing manhole or access point and an everting bladder is passed through the downtube, opened up and cuffed back over the mouth of the horizontal portion of the elbow and inserted into the collapsed liner. The collapsed liner within the existing conduit is then positioned over and secured to the cuffed back end of the inflation bladder. An everting fluid, such as water, is then fed into the downtube and the water pressure causes the inflation bladder to push out of the horizontal portion of the elbow and cause the collapsed liner to expand against the interior surface of the existing conduit. The eversion of the inflation bladder continues until the bladder reaches and extends into the downstream manhole or second access point. At this time the liner pressed against the interior surface of the existing conduit is allow to cure. Cure is initiated by introduction of hot curing water introduced into the inflation bladder in much the same manner as the recirculation line tied to the end of the everting bladder to cause the resin in the impregnated layer to cure.
After the resin in the liner cures, the inflation bladder may be removed or left in place in the cured liner. Both the pull-in and inflate method as well as the eversion method typically require man-access to restricted manhole space on several occasions during the process. For example, man-access is required to secure the everting liner or bladder to the end of the elbow and insert it into the collapsed liner.
Regardless of how the liner is to be installed a curable thermosetting resin is impregnated into the resin absorbent layers of a liner by a process referred to as “wet out.” The wet-out process generally involves injecting resin into resin absorbent layers through an end or an opening formed in the outer impermeable film, drawing a vacuum and passing the impregnated liner through nip rollers as is well known in the lining art. A wide variety of resins may be used, such as polyester, vinyl esters, epoxy resins and the like, which may be modified as desired. It is preferable to utilize a resin which is relatively stable at room temperature, but which cures readily when heated with air, steam or hot water, or subjected to appropriate radiation, such as ultra-violet light.
One such procedure for wetting out a liner by vacuum impregnation is described in Insituform U.S. Pat. No. 4,366,012. When the liner has inner and outer impermeable layers, the tubular liner may be supplied flat and slits formed on opposite sides of the flattened liner and resin injected and on both sides as described in the '063 patent. Another apparatus for wetting out at the time of installation while drawing a vacuum at the trailing end of the liner is shown in U.S. Pat. No. 4,182,262. The contents of each of these patents are incorporated herein by reference.
Recent efforts have been made to modify the pull-in and inflate method to utilize air to evert a bladder into the pulled-in liner from a proximal access point as described in U.S. Pat. No. 6,539,979 and application publication No. 2003/0015247 A1, the contents of which are incorporated herein by reference. When the everting bladder reaches the distal access point, steam is introduced into the proximal access point to initiate cure of the resin impregnated into the resin impregnable layer. This process offers the advantage of faster cure due to the increased energy carried by the steam as the curing fluid. However, the process still requires eversion of a bladder into the pulled-in impregnated liner.
Efforts to avoid this step of everting the bladder into the pulled-in liner include performing the eversion step above ground. For example, in U.S. Pat. No. 6,270,289, the process includes everting a calibration hose into a flat-lying lining hose above ground prior to pulling the hose assembly into the existing conduit. This process avoids the eversion below grade, but is severely limited into the length of lining that can be laid out above ground prior to pulling-in.
A further suggestion to avoid this eversion is to manufacture a liner having an inner coating and an outer coating so that a curing fluid can be introduced directly into a pulled-in liner. The disadvantages here involves the difficulty faced when trying to impregnate the resin impregnable material disposed between the inner and outer impermeable coatings. The outer coating remains essential for handling the impregnated liner and to allow the liner to be pulled into the existing conduit and the inner coating is desired to all for curing with the steam.
Notwithstanding the modifications to both the eversion and pull-in and inflate trenchless rehabilitation methods, both processes are labor intensive, require an eversion step and suffer from the increased costs associated with this. Accordingly, it is desirable to provide a method of trenchless rehabilitation that reduces cycle time and manhole entry and uses steam as the curing fluid to take advantage of the energy available to provide an installation method which is safer, faster and more efficient economically than current rehabilitation methods.